Hi Tony, Thanks for your note on Neville Shute and the engineering principle that you cannot push a rope (or chain). I have read and reread all of Neville Shute's books, the most famous being "On the Beach". My favourite is "No Highway" about a boffin studying metal fatigue in aircraft. His actions causing a hard grounding of the plane was based on based his esoteric research. This book was written around the time of the Comet crashes due to metal fatigue and the stress risers in the corners of the square windows in the Comet. At the NASS conference in Portland ME, we were described in the media as "boffins". I took no offence but recognized it as an apt description recognizing that our arcane abstruse interest sometimes leaves people bemused.
Regards, Roger Bailey From: [email protected] Sent: Friday, September 09, 2016 1:58 AM To: [email protected] ; Sundial List Subject: Re: Using linkages to draw curves on sundials Hi John, This query immediately brought to mind an interesting aside from the autobiography of Neville Norman, who wrote novels under the pen-name of Neville Shute, as he did not wish to trivialize his main profession as an aeronautical engineer. Working in the team of Dr. Barnes Wallis designing the airship R100, (the successful commercial opponent of the fatal government-controlled R101), he was given the job of stressing its 16-sided lightweight polyagonal frames, held rigid by wires. Working in pairs, to avoid careless inputs to their mechanical calculators, they would take many weeks to assess the stress pattern of each assembly of girders and wires based on an initial assumption. When, after much tedious labour, they found that one of the wires based on their first proposal was 'in compression' (have you ever tried pushing a chain?) he said "We would moisten our lips and begin all over again". Electronic computers would have achieved the ultimate solution to this problem in microseconds both almost within my lifetime. http://www.century-of-flight.net/Aviation%20history/coming%20of%20age/R101%20disaster.htm ----Original Message---- From: [email protected] Date: 07/09/2016 0:14 To: "Sundial List"<[email protected]> Subj: Using linkages to draw curves on sundials Good morning, While researching mechanisms of wire strainers used to tighten wires in fences, and trying to find the theoretical mechanical advantages of the different mechanisms, the first thing I learned was that "linkages" are the key to many of them. There's a whole branch of mechanics devoted to the theory of these things which involve a zillion combinations of pivots and links to achieve various purposes, usually to transmit motion in a specific manner. The best explanation I found was Slocum, A. (2008). Fundamentals of design. Topic 4. Linkages (http://web.mit.edu/2.75/fundamentals/FUNdaMENTALs%20Book%20pdf/FUNdaMENTALs%20Topic%204.PDF). 3.3 MB But my curiosity lead me further, to a more mathematical treatment. Unfortunately and for unknown reasons, the Jefferson Lab Library has removed the title page. Bizarre! I contacted the library and they gave me the full title etc. Svoboda, A. (1948). Computing mechanisms and linkages. MIT Radiation Laboratory Series, Volume 27. New York, McGraw-Hill. (https://www.jlab.org/ir/MITSeries/V27.PDF) (CAREFUL: 40.8 MB) Among other things, this book shows how you can use mechanical linkages of various forms to draw the curves of mathematical functions. And seeing that the curves on sundials are all defined by equations, I was wondering if anyone knows of any attempts to make a mechanical device of links and pivots specifically for generating sundial equations, and thus drawing sundials? It seems to be a feasible but complicated way of doing it, with some serious mathematics behind the linkages. I don't include sundial rulers in this, as they are not physically linked and pivotted. Similarly, I don't include CNC machining as this involves moving the tool / work using a pre-programmed series of x, y and z coordinates. And of course, 3-D printing is out. (And I still haven't figured out what sort of linkages are used in the wire strainers I'm studying!) Cheers, John John Pickard [email protected] --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
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